Non-ionic Polysaccharide Research Articles

Interpolymer Complexes of Water‐Soluble Nonionic Polysaccharides with Polycarboxylic Acids and Their Applications

AbstractLiterature data as well as our own experimental results devoted to the complexation of polycarboxylic acids with various water‐soluble polysaccharides (methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, starch, and dextran) by means of hydrogen bonding are systematized and analyzed. The specific peculiarities of interpolymer complexes based on polysaccharides‐polycarboxylic acids are demonstrated. The perspectives for the application of these interpolymer complexes are considered. It was shown that these materials possess good biocompatibility and adhesive properties. The promising directions for further study of interpolymer complexes between polycarboxylic acids and nonionic polysaccharides as well as existing gaps in the knowledge in this field are pointed out.Formation of compact IPCs and hydrophilic interpolymer associates.magnified imageFormation of compact IPCs and hydrophilic interpolymer associates.

Emulsifying properties of whey protein–dextran conjugates at low pH and different salt concentrations

The emulsifying behaviour of glyco-protein complexes of the non-ionic polysaccharide dextran (500 kDa) with whey protein isolate (WPI) have been investigated in systems containing (20 vol.% oil phase) medium-chain triglyceride oil, silicone oil, orange oil, and n-tetradecane under acidic and high electrolyte concentrations. Covalent coupling of protein to polysaccharide is achieved by dry heat treatment of protein+polysaccharide mixtures. Emulsions were made with WPI and whey protein isolate-dextran (WPI-DX) conjugate, and stability was followed by determining changes in average droplet size and extent of serum separation with time, with gum arabic (GA) chosen as reference emulsifier. The results show that the WPI-DX conjugate gives much better stability than the whey protein alone or GA under similar conditions. The improved emulsifying properties of WPI on complexing with dextran is probably due to the enhanced steric stabilization provided by the bulky hydrophilic polysaccharide moiety.

Durability of Boston Blue Clay in Waste Containment Applications

An experimental investigation of the durability of natural and polymer-amended Boston Blue Clay (BBC) used in waste containment applications was conducted. Durability was assessed in terms of hydraulic conductivity and crack formation in response to freeze-thaw- and desiccation-induced stresses. The polymers tested were nonionic polysaccharide (guar gum) and cationic polyacrylamide (PAM) with aqueous concentrations ranging from 0.25 to 8.00 g/L. BBC proved resistant to shrinkage cracks from desiccation, but susceptible to ice lensing from the application of freeze-thaw cycles. The saturated hydraulic conductivity of natural BBC increased from 5×10−5 to 1×10−3 cm/s after five freeze-thaw cycles. The saturated hydraulic conductivity for guar- and PAM-amended BBC also increased in response to freeze-thaw cycling; however, both the initial and final values were nearly an order of magnitude lower than those of natural BBC. In terms of crack formation as identified with computed topography scans, extensive ice lensing was observed in both the unamended and guar-amended specimens, while the PAM-amended specimen exhibited no such behavior in response to freeze-thaw cycling. Crack formation from either desiccation or freeze-thaw cycling was quantified in terms of a crack area density (CAD) that decreased for both guar- and PAM-amended specimens, as compared with the natural BBC. In particular, the observed CAD values for natural and PAM-amended BBC subjected to freeze-thaw cycling were 69 and 8%, respectively. The observed CAD values for all BBC specimens subjected to desiccation stress were less than 3%. Overall, these results indicate that natural BBC may be unsuitable for waste containment applications where control measures are not implemented for frost penetration. Moreover, polymer amendment serves to improve the material by reducing crack formation and hydraulic conductivity.

Direct Observation of Water−Oil Emulsion Systems in the Liquid State by Environmental Scanning Electron Microscopy

Environmental scanning electron microscopy is a technique capable of imaging fluid systems in their natural state without prior specimen preparation. As such, it is potentially a very powerful tool for studying emulsion structures at a resolution significantly higher than that for conventional optical microscopy. We present data on several water−oil emulsions that demonstrate the capability of the instrument. Separate preparations of vegetable oil and polybutene were used, emulsified with nonionic polysaccharide surfactants. Rather large contrast variations were found between the oil and water phases, with water always appearing brighter whether it was in the dispersed or continuous phase. The observed contrast is attributed to variations in the secondary electron emission characteristics arising from the dielectric response function of water compared with hydrocarbons. We propose that delocalized electrons in π-bonds provide an energy-absorbing mechanism that leads to a reduction in secondary electron emission from unsaturated hydrocarbon oils, relative to that of water, by lowering the energy gap. We present a qualitative description of an “energy window” model, affording secondary electrons a range of energies over which interactions with the sample are minimal, and discuss how variations of the energy window are likely to influence secondary electron emission.

The adsorption of a polysaccharide at the talc–aqueous solution interface

An investigation of the mechanism of adsorption of guar, a natural nonionic polysaccharide, at the talc–aqueous solution interface has been performed. Hydrophobic interactions were found to dominate the adsorption process, leading to adsorption of the guar onto hydrophobic sites, i.e. the talc “face”. Hydrogen bonding made only a small contribution to the adsorption, whilst chemical interactions were completely absent. In the case of ionically modified guars, the electrostatic contribution to the overall thermodynamics of adsorption was weak. Both unmodified and modified guars were found to adsorb in a very flat conformation with in excess of 75% of the constituent segments present in the form of “trains” at the talc–aqueous solution interface. Determinations of adsorbed layer thickness, calculated from microelectrophoresis measurements, supported this finding. The mannose backbone of the guar chain adsorbed to the talc surface, leaving the pendant galactose groups protruding into the bulk solution.

Using Secondary Electron Contrast for Imaging Water-Oil Emulsions in the Environmental SEM (ESEM)

Abstract The ESEM is able to image liquids in their natural state, unlike conventional SEM, and offers significantly better resolution than optical microscopy. The ability to image binary liquid mixtures, such as water-oil emulsions, depends upon sufficient contrast for differentiation of the dispersed and continuous phases. We have made observations of such water-oil emulsions in an Electroscan 2010 Environmental SEM, and have duly obtained images with good contrast. Experiments were carried out on emulsions of vegetable oil-in-water, polybutene-in-water and water-in-polybutene, all emulsified with nonionic polysaccharide surfactants. Each sample was imaged at a temperature of approximately 3°C, in water vapour at a pressure of 4 torr, in order to maintain the liquid state. From the ESEM micrographs in Figures 1, 2 and 3, it is clear that water exhibits a greater secondary electron emission than an unsaturated hydrocarbon.

Foam stabilization by protein-polysaccharide complexes

Abstract Foaming properties of covalent complexes of the nonionic polysaccharide dextran with three proteins (bovine serum albumin (BSA), lysozyme, β-casein) have been investigated by monitoring small pressure changes above collapsing foams in a closed chamber. Assessment of foamability has been based on (i) the total foam volume produced and (ii) the pressure change associated with total foam collapse. Foam stability has been assessed in terms of (i) the time for loss of half the foam volume and (ii) the first-order rate constant associated with the time-dependent pressure change. The differential pressure monitoring technique has been found to be a more sensitive method of measuring foamability than the simple foam volume determination. A good correlation has been found between foam stability results based on the pressure monitoring technique and those based simply on the rate of foam volume collapse. Protein-polysaccharide hybrids were prepared by extended dry heating of mixtures of protein and polysaccharide at 60°C under conditions of controlled relative humidity (40% or 79%). Foams were produced from dilute aqueous solutions of protein or protein-polysaccharide complex at pH 7 by sparging with nitrogen gas at constant temperature (15–30°C). It has been found that complexation of lysozyme with dextran leads a very substantial enhancement in foaming properties, whereas complexation with BSA leads to only a small improvement, and complexation with β-casein has a negative effect. The effects of complexation were enhanced with increasing molecular weight of the polysaccharide. In accordance with earlier work on emulsifying properties of similar hybrids, it appears that there is an optimum dry-heat treatment time for the enhancement of protein functionality by covalent complexation.

Polysaccharides at interfaces 2. Surface potential of adsorbed cholesteryl-pullulan monolayers at the solution-air interface

The surface potential of adsorbed monolayers of cholesteryl-pullulan (CHP) derivatives has been determined by the ionizing differential electrode method. It has been found that this potential is highly dependent on the degree of cholesterol grafted onto pullulan, and that the native polysaccharide displays neither surface activity nor surface potential. As the disordered structure of the non-ionic polysaccharide unit generates a random orientation of intrinsic dipole moments, it has been considered that its contribution to the measured surface potential is rather small, compared to the cholesteryl group dipolar contribution. The surface densities of cholesteryl groups of adsorbed CHP molecules have been determined from the relationship between the surface potential and the surface density of spread cholesterol molecules. The assessment of these quantities was essential, as the determination of the surface tension data for the CHP derivatives with low cholesteryl content (CHP 45−0.6 and CHP 50−0.9) was difficult to achieve (Part I of this work [B. Deme´, V. Rosilio and A. Baszkin, Colloids Surfaces B: Biointerfaces, 4 (1995) 357]). These results complement those from the surface tension measurements, and confirm that in the surface layer of the adsorbed polysaccharide the ordered cholesteryl groups are oriented towards the air phase and the disordered polysaccharide is immersed in the aqueous subphase. Proposed models for semi-organized adsorbed CHP layers are discussed.

Osmotic Pressure, Creaming, and Rheology of Emulsions Containing Nonionic Polysaccharide

We report measurements of the osmotic pressure, rheology, and creaming of concentrated oil-in-water emulsions (30 wt% mineral oil, 1 wt% surfactant, pH 7, ionic strength 0.05 M) as a function of the concentration of added nonionic polysaccharide dextran (5 × 105 Da). Experiments were carried out at 25°C on emulsions prepared with two different low-molecular-weight surfactants—nonionic Tween 20 (polyoxyethylenesorbitan monolaurate) and anionic SDS (sodium dodecyl sulfate). For both types of emulsifier, the addition of dextran was found to lead to a reduction in osmotic pressure, an increase in the limiting zero-shear-rate viscosity, and an enhancement in the rate of serum separation. These observations are consistent with the theory of depletion flocculation of the droplets by the nonadsorbing polymer. The effects of the surfactant type on emulsion properties are most evident at low or high dextran contents. The results are compared with those reported earlier for the same emulsions containing the anionic polysaccharide rhamsan. The combined data indicate a strong but complex relationship between creaming stability and low-stress creep rheological behavior. Substantial differences in properties between emulsions made with nonionic and charged surfactants indicate the importance of surfactant-biopolymer interactions in controlling the flocculation of emulsion droplets.

Adsorptive interaction of Ficoll standards with porous glass size-exclusion chromatography columns

Ficoll, a densely branched non-ionic polysaccharide, whose hydrodynamic properties resemble those expected for compact spheres, is an interesting material for fundamental studies of permeation in chromatographic and porous media. Calibrating porous glass size-exclusion chromatography columns with Ficoll, we found unexpected retention of this solute in salt solution, but normal behavior in nearly pure water (0.003 M, pH 7.0 sodium phosphate buffer). These chromatographic results, along with the findings of adsorption studies and viscometric measurements, can be best explained on the basis of sodium ion binding to Ficoll and consequent adsorption of the transient pseudo-polycation thus formed.

Phase separation involving ordered biopolymer systems

Abstract

Nonionic polysaccharides as calibration standards for aqueous size exclusion chromatography

Size exclusion chromatography may be used to determine molecular size or mass of solutes. The validity of the method depends on the correct choice of macromolecular standards used to calibrate the chromatographic column. This calibration is an experimental determination of the relationship between the molecular dimensions and the peak migration velocity of the solute, in practice often presented as a semi-logarithmic plot of log( MW) vs elution volume, but more fundamentally expressed as the dependence of for example, the Stokes radius ( R S), or the viscosity radius ( R η ) on the chromatographic partition coefficient, K SEC. The validity of this calibration rests on the absence of enthalpic interactions between the standards and the stationary phase and the ability to determine the standards' molecular dimensions and/or mass in a nonambiguous way. Nonionic polysaccharides are ideal for this purpose, and furthermore provide an excellent paradigm for studying the role of molecular architecture in the relationship between K SEC and R η or R S.

Determination of protein foam stability from time-dependent pressure monitoring

An apparatus is described for the determination of protein foam stability from time-dependent measurements of the small pressure changes above the collapsing foam in a closed chamber. Experimental data are reported for foams made with a fixed concentration (0.1% wt) of bovine serum albumin (BSA) and various concentrations of the nonionic polysaccharide dextran at neutral pH. The results show a loss of foam stability at low dextran contents, an increase in stability at high contents, and a minimum level of stability at a dextran:bovine serum albumin (BSA) molar ratio of ~2. The trends in the data obtained with the new pressure monitoring apparatus are consistent with those obtained by visual observations of the rate of foam volume decay.

Quantitation of non-ideal behavior in protein size-exclusion chromatography

The size-exclusion chromatographic partition coefficient ( K sec) was measured on a Superose 6 column for three sets of well-characterized spherically symmetrical solutes: the compact, densely branched non-ionic polysaccharide, Ficoll; the flexible chain non-ionic polysaccharide, pullulan; and compact, anionic synthetic polymers, carboxylated starburst dendrimers. All three solutes display a congruent dependence of K sec on solute radius, R. In accord with a simple geometric model for SEC, all of these data conform to the same linear plot of K SEC 1/2 vs. R. This plot reveals the behavior of non-interacting spheres on this column. Comparison of results for a number of globular proteins at various pH values to this “ideal” curve allows a quantitative measure of protein attraction or repulsion. It is shown that the usual procedure of obtaining a “best-fit” curve for a set of proteins is likely to generate an erroneous calibration curve.

Body distribution profile of polysaccharides after intravenous administration

AbstractThe body distribution of pullulan and dextran, which are nonionic polysaccharides, was studied. After intravenous injection of 125I-labeled polysaccharides with different molecular weights, the half-life period in the blood circulation and the body distribution were pharmacokinetically investigated and compared with those of polyethylene glycol (PEG) and polyvinyl alcohol (PVA). Polysaccharides of higher molecular weights circulated in the bloodstream for a longer period than those of lower molecular weights. The half-life period of pullulan ranged from 15 to 90 min, changing remark-ably around molecular weight 30,000, and was shorter than that of dextran. Body distribution studies demonstrated that pullulan tended to accumulate in the liver to a greater extent than dextran, whereas PEG and PVA were hardly disposed there. This preferable accumulation of polysaccharides in the liver was observed over the whole molecular weight range studied. Eighty percent of pullulan with large molecular weights w...

Emulsifying properties of covalent protein—dextran hybrids

The emulsifying behaviour of covalent Maillard complexes of the non-ionic polysaccharide dextran with three proteins (11S globulin Vicia faba, bovine serum albumin, β-casein) has been investigated as a function of the molecular weight of the dextran (4 · 10 4 or 5 · 10 5 Da) and the polysaccharide/protein molar ratio R. Protein—polysaccharide hybrids are made by dry-heating mixtures of protein and dextran at 60°C for (usually) 3 weeks. The droplet-size distribution and serum layer thickness are monitored as a function of storage time for oil-in-water emulsions (10 vol.% n-tetradecane 0.5 wt.% protein. pH 8, ionic strength 0.1 M) containing various proportions of polysaccharide, present either as a Maillard complex or in a simple admixture with the protein. The results show that covalent binding of dextran to the globular proteins (bovine serum albumin and 11S globulin) can lead to a substantial improvement in the emulsifying behaviour, whereas complexation with the disordered protein β-casein has a negative effect. The globulin—dextran hybrids generally give much finer emulsions than the 11S globulin alone which is a rather poor emulsifying agent. For each protein, the emulsifying capacity and emulsion stability are sensitive to dextran molecular weight and R, and it appears that for each protein—polysaccharide combination there is a critical value of R which confers the optimum stabilization. Reaction of protein with dextran for longer than is necessary (especially that of high molecular weight) leads to loss of functionality, as does the presence of unadsorbed (unreacted) polysaccharide. The primary single reason for the improved emulsifying properties of globular proteins on complexing with polysaccharide is the enhanced steric stabilization provided by the bulky hydrophilic polysaccharide moiety. As the measured surface shear viscosity of the adsorbed globulin—dextran hybrid is only slightly different from that of the adsorbed native protein alone, it appears that the protein—protein interactions in the adsorbed layer are relatively unaffected by the complexation.

Emulsion stabilization by ionic and covalent complexes of β-lactoglobulin with polysaccharides

The influence of protein—polysaccharide interactions on the surface and emulsifying properties of β-lactoglobulin at pH 7 has been investigated for systems containing the non-ionic polysaccharide dextran, and the anionic polysaccharides dextran sulphate and propylene glycol alginate (PGA). Tension measurements at the n-hexadecane—water interface are indicative of complex formation with dextran sulphate or PGA, but not with dextran. Emulsions made with simple 1:1 mixtures of protein + polysaccharide (0.5 wt% protein, 10 wt% n-hexadecane) give poorer stability than with protein alone under similar conditions. The presence of unadsorbed polysaccharide gives rapid serum separation due to depletion flocculation. Of the three polysaccharides, PGA gives the largest droplets in the fresh emulsion, but the best stability with respect to coalescence; this is consistent with the formation of a weak protein—PGA complex at the oil—water interface. An attempt has been made to produce strong complexes of β-lactoglobulin with each of the polysaccharides by dry-heating the mixtures at 60°C for up to 3 weeks. This treatment yields a β-lactoglobulin-dextran hybrid which is believed to contain a covalent Maillard-type linkage between the two biopolymers, and which gives emulsions with excellent stability with respect to creaming, coalescence and serum separation. A β-lactoglobulin—dextran sulphate composite produced by the same dry-heating treatment shows little evidence for Maillard-type browning and has poor emulsifying properties. Dry-heating of a mixture of β-lactoglobulin and PGA gives a complex that confers emulsion stability which is at least as good as that for the β-lactoglobulin-dextran hybrid. These results show that protein—polysaccharide emulsifiers with good solubility and excellent emulsion stabilizing properties at pH 7 can be made with food-grade ingredients without the use of chemicals.

Improved resolution of DNA fragments in polysaccharide-supplemented agarose gels

The electrophoretic separation of nucleic acids, including small DNA fragments in the range 50–1000 bp, is presently carried out in polyacrylamide gels or in gels containing high concentrations of agarose. We have developed an alternative gel matrix composition which is inexpensive, nontoxic, easy to prepare, and highly transparent to visible and uv light. The composition combines a soluble nonionic polysaccharide such as hydroxyethylcellulose, methylcellulose, or galactomannan with a minimum but sufficient concentration of agarose to form a gel which immobilizes the “liquid phase sieve.” These mixtures do not replace polyacrylamide for resolving fragments smaller than approximately 75 nucleotides. However, the new gels show DNA fragment resolution (band separation versus distance traveled) and optical clarity superior to those of conventional agarose.